Process for the annealing of precipitation hardening alloys

ABSTRACT

There is provided an annealing process for the production of a clean, flat CuBe product in conjunction with the production of precipitation hardenable alloys. These alloys have to be rapidly cooled from an annealing temperature to prevent precipitation of the hardening constituent. Historically, this has been done by water quenching, which results in a badly distorted and buckled product. As a result, special or additional processing steps such as temper rolling or roll leveling have to be employed in order to successfully process the material. The invention stated here provides a process which eliminates these problems by rapidly cooling the material with a gaseous atmosphere; i.e., by using a &#39;&#39;&#39;&#39;gas quench.

United States Patent De J arnett PROCESS FOR THE ANNEALING OF PRECIPITATION HARDENING ALLOYS US. Cl l48/l3.2, l48/l1.5 R, l48/l2.7, l48/20.3, 148/160 Int. Cl. C22f l/02 Field of Search 148/13, 13.2, 16, 20.3, 148/158-l62, ll.5 R, 212.3, l2.7

References Cited UNITED STATES PATENTS Klement 148/160 Smith l48/ll.5 R

[4 1 Oct. 15, 1974 Primary ExaminerR. Dean Attorney, Agent, or F irm-McNenny, Farrington, Peame & Gordon [5 7 ABSTRACT There is provided an annealing process for the production of a clean, flat CuBe product in conjunction with the production of precipitation hardenable alloys. These alloys have to be rapidly cooled from an annealing temperature to prevent precipitation of the hardening constituent. Historically, this has been done by water quenching, which results in a badly distorted and buckled product. As a result, special or additional processing steps such as temper rolling or roll leveling have to be employed in order to successfully process the material. The invention stated here provides a process which eliminates these problems by rapidly cooling the material with a gaseous atmosphere; i.e., by using a gas quench.

6 Claims, 2 Drawing Figures PROCESS FOR THE ANNEALING OF PRECIPITATION HARDENING ALLOYS BACKGROUND OF THE INVENTION AND PRIOR ART In general, this invention relates to a process for the production of alloys which are hardenable by precipitation of a phase from solid solution. More specifically, it relates to the production of annealed CuBe alloy products, such as sheet, plate, strip or foil, round-and flat wire, which are flat. Even more specifically, it relates to the quenching step in the annealing process used for the production of the above mentioned products.

The most effective hardening of alloys, by a precipitation hardening mechanism, is accomplished by controlled precipitation of the hardening phase from solid solution. To a large extent, many of the important properties of the hardened alloy can be varied through proper control of the system parameters while precipitation is occurring. In virtually all cases, adequate control of the precipitation reaction can be achieved only if the entire amount of this hardening phase is in the solid solution state, so that the entire precipitation process can be controlled. As a result, effective hardening through precipitation from solid solution involves three steps; namely,

l. Solutionization of the phase which ultimately produces the hardening effect; i.e., putting this phase into solid solution by soaking" the material at an elevated temperature;

2. Quenching of the material from the solutionizing temperature to a temperature at or below the temperature of the aging process described below in item (3). Quenching (rapid cooling) is required to retain the phase in solid solution during the cool-down part of the cycle between solutionizing and aging. Normal practice is to liquid quench the material well below the aging temperature.

3. Aging the material, which is the process of permitting the phase to precipitate under'controlled conditions. Time and temperature are especially important parameters.

In the state of the art, the combined steps of (1) and (2) are referred to as the annealing or solutionannealing process. At the soaking temperatures used for CuBe alloys (approximately 1,450F. or l,700F. depending upon beryllium content), two different processes are occurring simultaneously when standard roll-mill products are involved. Rolling produces workhardening in the material which causes an annealing process (recovery and/or recrystallization reactions) to take place at elevated temperatures. Solutionizing of the phase, which eventually causes the hardening effect, also occurs.

For the purpose of the invention described herein, the annealed condition is that condition resulting from the combined steps of (l) and (2) described above.

This annealing process is the one that the present invention relates to.

During the quenching step, the object from a theoretical standpoint is to cool the material from the solutionizing temperature very rapidly, to ensure that the precipitation reaction does not occur prematurely to any significant degree. In practice, the common procedure is to quench the material in a liquid, usually water, to

ensure that cooling will occur at a faster rate than the minimum allowable rate. This process results in a satisfactory metallurgical anneal, but the product, particularly strip or sheet, is badly distorted and buckled. This necessitates special or additional processing steps such as temper rolling or roll leveling to successfully process the material to completion.

The primary object of thisinvention is to provide an adequate quenching process for the annealing of rolled precipitation hardening alloys in the various forms described herein, which will minimize the distortion produced by rapid cooling, thereby eliminating additional processing steps for flattening the annealed product. This is accomplished by using a gas quench as opposed to a liquid quench.

An additional advantage can be realized relative to the removal of the oxidation film which forms on the product during the annealing process. Removal of this film is difficult, especially for CuBe alloys. A pickling operation is required for its removal when the product is distorted, such as that which results when a liquid quench is used. Prior art shows that Pechiney has applied for a patent (Germany-Publication No. 1,621,142.?) relating to a pickling process for CuBe alloys. I

Since the annealed strip is relatively flat when a gasquench is employed, an optional method for the removal of the surface oxide film can be realized. Light grinding, polishing or other similar abrasive methods can be used. Elimination of the pickling operation and the subsequent problems of waste disposal can be very advantageous.

In addition to distortion, water quenching produces a second problem. Contamination of the furnace atmosphere with water vapor (or other vapors) promotes the formation of an oxidation film. Regardless of which removal method is employed for this film, an annealed product having a minimum oxidation film is highly desirable.

Prior art includes the patent to E. M. Smith US. Pat. No. 3,138,493 for a Method of Heat Treating Beryllium Copper Alloys. One should recognize that his invention relates to step (3) described above; namely, the aging process. Aside from the resulting metallurgical differences, these two processes differ significantly relative to the temperature at which they are carried out. Annealing at approximately l,450F. or 1,700F., as may be required by specific levels of beryllium, produces problems which are not encountered in the aging temperature range of 525-825F. At the higher temperature, oxidation isenhanced. In addition, the distortion produced by a water quench is more severe.

BRIEF STATEMENT OF THE INVENTION In accordance with the objectives and advantages stated herein, the invention comprises a process for the annealing of rolled precipitation hardening alloys through use of a gaseous media for rapid cooling of the material from the solutionizing temperature; i.e., by employing a gas quench instead of the heretofore liquid quench. By quenching" the material in a controlled gaseous atmosphere which is similar to that used in the furnace during the solutionizing step, contamination of the furnace atmosphere with constituents that promote oxidation (such as water vapor) is drastically reduced. A gaseous quench can result in the production of a flat annealed product, thereby eliminating the flatten- I pickling, the film can be removed by use of abrasives.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE DRAWINGS AND PROCESS The cooling chamber is best shown in FIG. 1. As indicated therein, the alloy strip is rapidly cooled by gas quenching to a temperature below about 250F. by directing many high velocity jets of cooling gas against the top and bottom surfaces of the alloy material. The nature of the cooiinggas is not critical although it is desirable that it have the-same composition as that used inthesolutionizing furnace. Any inert or nonoxidizing gas maybe used. It will be noted that the system is generally closed and that the gases used in cooling are continuously recirculated and cooled within the system for redistribution to. the top and bottom surfaces of the v alloy strip being 'q uenched.

' Accordingly, there is provided a support framework in. which is supported by any suitable means a boxlike enclosedcooling chamber 12 having suitably supported therein an upper plenum 14 and a lower plenum l6. A lso supportedwithin the chamber 12 are a pluralof belts 46 to drive pulleys 48 mounted on shaft 50 for rotation of the fan element.

The outlet 40 of the blower36 is suitably connected to a Y-section 52' communicating with upper plenum supply duct 54 and lower plenum supply duct 56.

. Upper plenum supply duct. 54 conducts aboutone-half ity of rollers 18 suitably spaced for carrying the strip 20 between the plenums 14and 16.

The chamber 12 is provided, with a closed bottom 22 and a gas-collecting hood 24 having a flanged outlet 26 mounted at one end thereof. Superimposed over the flanged opening 26 there is provided a cooling section 28. The cooling section 28 is suitably sized and flanged for fitting onto the conduit defined by the opening 26.

Within the section 28, there are supported cooling coils 30 of adequate heat exchange design and capacity to reduce the temperature of the gas collected in the hood 24 and flowing through the flanged opening 26 from a temperature of upto 160F. to a temperature preferably below about 100F. Suitable means of conventional design and operation, not shown, are provided for introducing cooling fluid, preferably cooling water, into and out of the coil 30 as shown by the arrows in FIG. 1. This section of the gas conduit is conveniently rectangular in cross-sectional configuration and is surmounted by a transition section 32 of the conduit which adapts the rectangular configuration of the'cooling section 28 to the circular cross-section of a return duct 34. The return duct 34 is in turn connected to a blower'36fitted with a flanged inlet 38 and a flanged outlet-40. The blower 36 is desirably a centrifugal fan of conventional design and operation having a gas-tight shaft seal. A suitable motor42 such as a fivehorsepowe'r 3600 rpm electric motor is suitably mounted on a support structure generally indicated at 440i any suitable construction which is in turn carried by the frame 10. The motor 42 is connected by means sired, the oxidation film can be removed at this point of the outputof the blower36 tothe upper plenum 14 through a suitable opening 58, and lower plenum supply duct 56 supplies the remaining volume of cooling gas from the blower 36 to the lower plenum 16 through a suitable opening 60 therein. a

Plenums 14 and 16 are tapered box-like. structures of decreasing cross-sectional area in a direction proceeding away from th inlets 58 and 60, respectively. These structures are closed except for the openings 58 and 60, and except for the perforated plates 62 and 64 which are disposed in confronting relation with the upper and lower surfaces, respectively, of the alloy strip 20. In the embodiment shown, the plenums 14 and 16 are approximately 3 feetlong by 22 inches wide as shown inFIG. '2, andthe holes 66 through which high velocity jets of cooling gas. are directed toward the upper and lower surfaces of the strip 20 are one-half inchv diameter holes distributed on two-inch centers and covering the entire surface of the plates 62 and 64, respectively. In the embodimentshowmthe perforated surfaces or plates 62 and64 are spaced. from the strip 20 approximately 3 inches, respectively. Gas for cooling is forced through the openings 66 in both the plenums 14 and 16 onto the major surfaces'of the alloy strip 20 at a velocity generally in the range of from 300 to 600 feet per minute, and preferably about 400 feet per Y minute;

FIG. 2-shows the flow of the cooling gases over the upper and lower surfacesof the strip or ribbon 20, the collection of the heated gases in the hood 24, and their passage through the flanged opening 26. The heated gases, now at a temperature of approximately to 160F. then contact the cooling coils 30 where the temperature isreduced to preferably lO0F or below. The fan 36 then recirculates the-cooled gases back through the plenums 14 and '16 as indicated above.

v -'The apparatus shown in FIGS. 1 and 2 is adapted for location in contiguous relationshipwith a solutionizing furnace for a precipitation hardenable alloy strip, such as copper/beryllium alloy containing less than about 2% beryllium. The exit from such a solutionizing furnace is generally indicated at 68. Solutionizing furnace 68 forms no part of the invention in the apparatus and is of conventional known structure. Between the furnace exit 68 and cooling chamber 12, there is provided damping means including a damper housing 74, a graphite block 76, and a damper block of graphite 78 vertically adjustably movable in a damper guide 80.

The damper block 78 in conjunction with the bed block of graphite 76 prevents the gas from the cooling chamber from cooling off the discharge end of the furnace. The strip 20 enters the cooling chamber 12 through a slit 70 and exits therefrom through a slit 72.

At the exit from the cooling chamber, adjacent the slit 72, there is provided an elongated box-like exit seal including a fabric lined slit 84. The temperature of the strip as it emerges from the slit 84 is about F. The strip 20 may then proceed to a coiler, not shown, and of conventional structure passing bya guide roll 86 in so doing and changing direction therearound. If deby an abrasive method, since the strip is adequately free from distortion.

In a specific example, a ribbon of copper/beryllium alloy solutionized in the furnace 68 at a solutionizing temperature of approximately 1,450F. is continuously pulled through the cooler, as shown. While in the cooler, it runs at a rate of 3 feet per minute between the two plenum chambers 14 and 16, each of which is approximately 3 feet long. The top of the bottom plenum 16 and the bottom of the top plenum 14 are formed of perforated plates 62 and 64 wherein the holes are onehalf inch in diameter and located on two-inch centers. The gas (recycled exothermic atmosphere) is discharged through these holes at a velocity of approximately 400 feet per minute and impinges directly upon the strip 20. The residence time in the gas quenching chamber 12 is about 60 seconds. The residence time in practice hereof is only that which, under the conditions of strip velocity, gas temperature, strip inlet temperature, etc., is required to rapidly cool the alloy below the precipitation temperature, for example below about 200F.

The gas is then passed over a finned tube cooling coil 30 and is recirculated by the blower 36 back to the distribution plenums 14 and 16.

For a 16-inch wide by 0.035-inch copper/beryllium strip traveling at a rate of 3 feet per minute, the gas is heated to approximately 120F. while passing over the strip. It is cooled to approximately 95F. by the cooling coil 30. The pressure drop across the strip and the coil is approximately 3 inches of water and the volume of atmosphere circulated is approximately 2,000 cubic feet per minute.

The strip is in the cooling chamber 12 approximately one minute and exits from the cooler at a temperature of 140F. maximum, which is well below the precipitation temperature and yields a supersaturated solid solution of the alloy. This may then be reheated to the conditions for controlled precipitation hardening. An example of such aging procedure is given in the aforementioned U.S. Pat. No. 3,138,493. In general, the aging process is carried out at a temperature not in excess of about 900F. and above about 600F., depending upon beryllium content, for a period of time between about 2 minutes and 3 hours. The time and temperature are related in the usual way and will also be determined by the final desired properties.

Suitable copper/beryllium alloys contain from 0.50 to 2.05 percent beryllium, balance copper, and may additionally include minor amounts of cobalt (approximately 0.25 to 2.5 percent). Strips of copper/beryllium alloy ranging in thickness from 0.010 to 0.060 inches have been satisfactorily gas quenched in the apparatus shown in FIGS. 1 and 2. These strips show no distortion by reason of rapid quenching in a gas stream from solutionizing temperature to a temperature of approximately 140F.

While the invention has been illustrated with respect to copper/beryllium alloys, it is useful in the processing of other precipitation hardening alloys which are well known to those skilled in the art. Instead of air as the cooling agent which often results in oxidation, it is desirable to use the same nonoxidizing or reducing atmosphere as is used in the solutionizing furnace. Continual recirculation of these gases can be an economical advantage.

What is claimed is:

l. A process for annealing a rolled sheet of precipitation hardening copper beryllium alloy with minimum distortion which comprises the steps of:

a. solutionizing a strip of a precipitation hardenable copper-beryllium alloy at a temperature of from 1,450F to l,700F; and

b. quenching said strip rapidly to a temperature below about 250F by passing said strip through a nonoxidizing gas quenching zone between a multitude of oppositely directed gas jets impinging on the respective surfaces of said strip, the inlet temperature of said gas being below about l00F.

2. A process in accordance with claim 1 wherein the solutionizing step is carried out in a nonoxidizing gas atmosphere and in which the quenching gas is the same as that used for the solutionizing step.

3. A process in accordance with claim 1 in which the alloy isa copper/beryllium alloy containing from 0.5 to 2.05 percent beryllium, balance copper.

4. A process in accordance with claim 3 in which the alloy also contains cobalt in the amount of about 0.25 to 2.50 percent.

5. A process in accordance with claim 1 which is additionally characterized by the step of aging the solutionized and quenched strip at a temperature not in excess of about 900F. and above about 600F. for a period of time between about 2 minutes and 3 hours.

6. A process in accordance with claim 1 in which the gas is impinged on the respective surfaces of the strip at a velocity in the range of from 300 to 600 feet per minute. 

1. A PROCESS FOR ANNEALING A ROLLED SHEET OF PRECIPITATION HARDENING COPPER BERYLLIUM ALLOY WITH MINIMUM DISTORTION WHICH COMPRISES THE STEPS OF: A. SOLUTIONIZING A STRIP OF A PRECIPITATION HARDENABLE COPPERBERYLLIUM ALLOY AT A TEMPERATURE OF FROM 1,450*F TO 1,700*F, AND B. QUENCHING SAID STRIP RAPIDLY TO A TEMPERATURE BELOW ABOUT 250*F BY PASSING SAID STRIP THROUGH A NONOXIDIZING GAS QUENCHING ZONE BETWEEN A MULTITUDE OF OPPOSITELY DIRECTED GAS JETS IMPINGING ON THE RESPECTIVE SURFACES OF SAID STRIP, THE INLET TEMPERATURE OF SAID GAS BEING BELOW ABOUT 100*F.
 2. A process in accordance with claim 1 wherein the solutionizing step is carried out in a nonoxidizing gas atmosphere and in which the quenching gas is the same as that used for the solutionizing step.
 3. A process in accordance with claim 1 in which the alloy is a copper/beryllium alloy containing from 0.5 to 2.05 percent beryllium, balance copper.
 4. A process in accordance with claim 3 in which the alloy also contains cobalt in the amount of about 0.25 to 2.50 percent.
 5. A process in accordance with claim 1 which is additionally characterized by the step of aging the solutionized and quenched strip at a temperature not in excess of about 900*F. and above about 600*F. for a period of time between about 2 minutes and 3 hours.
 6. A process in accordance with claim 1 in which the gas is impinged on the respective surfaces of the strip at a velocity in the range of from 300 to 600 feet per minute. 